1. Field of the Invention
This invention relates to synthetic absorbable sutures, and more particularly, to synthetic absorbable sutures comprising extruded and oriented filaments of copolymers of polyoxalates having isomorphic sequences.
2. Description of Prior Art
Absorbable suture materials have traditionally been natural collagenous materials obtained from sheep or beef intestine, commonly known as catgut. More recently, it has been proposed to manufacture synthetic absorbable sutures from polyesters of hydroxycarboxylic acids, notably polylactide, polyglycolide, and copolymers of lactide and glycolide. Such synthetic absorbable sutures are described in U.S. Pat. Nos. 3,636,956 3,297,033 and elsewhere in the literature. Polyesters of succinic acid have also been suggested for at least partially bioresorbable surgical articles as disclosed for example in U.S. Pat. No. 3,883,901.
Among the requirements of an ideal absorbable suture are that it should have good handling properties, should approximate and hold tissue for proper healing with minimal tearing and tissue damage, should have adequate straight tensile and knot strength, should be controllably uniform in properties including dimensional stability within the body, should be sterilizable, should be absorbable by living tissue, preferably at a constant rate regardless of the place in the body or the condition of the patient and without causing such unfavorable tissue reactions as walling off, granuloma formation or excessive edema, and finally should be capable of being properly and easily tied into surgical knots.
While multifilament sutures manufactured from polymers of lactide and glycolide fulfill the above requirements to a large degree, monofilament sutures of these materials are considerably less flexible than catgut and these synthetic sutures are accordingly generally limited to a multifilament, braided construction. Sutures of glycolide polymers are also not suitable for sterilization by radiation without suffering severe degradation of physical properties.
We have discovered that copolyoxalate copolymers having isomorphic sequences can be melt extruded into pliable, monofilament fibers which have good in vivo strength retention and are absorbed in animal tissue without significant adverse tissue reaction. The fibers have good tensile and knot strength, and can be sterilized by gamma radiation without serious loss of these properties. In addition, monofilament sutures of the polymers of the present invention have a high degree of softness and flexibility not found in many synthetic absorbable sutures of the prior art.
The preparation of polyoxalate polymers is described in the art. Carothers et al, J. Amer. Chem. Soc. 52, 3292 (1930) for example, describes the ester interchange reaction of diols such as ethylene glycol, 1,3-propanediol, or 1,4-butanediol with diethyl oxalate to yield a mixture of monomer, soluble polymer and insoluble polymer. The reaction of oxalic acid and an alkylene glycol to form polyester resins is described in U.S. Pat. No. 2,111,762, while the preparation of polyesters of fiber-forming quality from dicarboxylic acids and diols is described in U.S. Pat. Nos. 2,071,250-1 and 2,952,652. Isomorphic polymers including polyester copolymers have been discussed in the literature.sup.(1). The particular isomorphic copolyoxalates of the present invention however, have not previously been known, nor has their preparation or use as synthetic absorbable sutures been suggested heretofore.
It is accordingly an object of the present invention to provide new and useful polymers of isomorphic copolyoxalates and articles made therefrom. A further object of this invention is to provide synthetic absorbable sutures of isomorphic copolyoxalates. It is a yet further object of this invention to provide surgical aids and prostheses fabricated of fibers or cast or machined from blocks of isomorphic copolyoxalate polymers.